The invention relates to a security element in the form of a multilayered film body having a volume hologram layer, and to a method for producing such a security element.
Holograms are used as security elements for protecting security documents such as banknotes, money substitutes, credit cards, passports or ID documents and also for product protection. In mass-produced products, surface holograms are often used, by means of which interesting optically variable effects, for example movement effects, can be obtained and which are distinguished by a high luminous intensity.
Volume holograms, also referred to as white light holograms, in contrast to surface holograms, are based on diffraction of light at the Bragg planes of a transparent layer having local differences in refractive index.
A security element comprising a volume hologram and the production of such a security element are described for example by DE 10 2006 016 139 A1. In order to produce a multilayer body containing a volume hologram, a surface relief is used as master. The front side of the master is brought into contact with the photosensitive layer of the multilayer body directly or with interposition of a transparent optical medium, in which photosensitive layer the volume hologram is intended to be recorded. Afterward, the master is exposed with coherent light, an interference pattern being formed by the superimposition of the light radiated onto the master and the light diffracted by the master, which interference pattern is recorded in the photosensitive layer as a volume hologram. The volume hologram introduced into the photosensitive layer in this way is then fixed after the curing of the photosensitive layer. By means of a specific configuration of the master, two or more separate image information items can be written into the photosensitive layer in this case.
Further, EP 1 187 728 B1 describes the lamination of two volume hologram layers one on top of the other, in which layers image information items have been written by means of different holographic recording methods. For the observer this gives rise to an overall impression composed of the image information items of the two volume hologram layers.